The above referenced related patent applications disclose multi-sensor guidewires and multi-sensor micro-catheters for use in interventional cardiology. For example, if a heart valve is found to be malfunctioning because it is defective or diseased, minimally invasive methods are known for repair and replacement of the heart valve, by introduction of a catheter intravascularly into the heart to access the heart valve. Percutaneous procedures for minimally invasive transcatheter heart valve diagnosis, repair and replacement avoid the need for open heart surgery. These procedures may be referred to as Transcatheter Valve Therapies (TVT).
TVT for valve repair include, for example, procedures such as, balloon valvuloplasty to widen an aortic valve which is narrowed by stenosis, or insertion of a mitral clip to reduce regurgitation when a mitral valve fails to close properly. Alternatively, if the valve cannot be repaired, a prosthetic replacement valve may be introduced. Minimally invasive Transcatheter heart Valve Replacement (TVR) procedures, including Transcatheter Aortic Valve Implantation (TAVI or TAVR) and Transcatheter Mitral Valve Implantation (TMVI), have been developed over the last decade and have become more common procedures in recent years.
While there have been many recent advances in systems and apparatus for TVT and for related diagnostic procedures, interventional cardiologists who perform these procedures have identified the need for improved apparatus for use in TVT, including apparatus for heart valve replacement. They are also seeking improved diagnostic equipment that provides real-time direct measurements, i.e. within the heart, of important hemodynamic cardiovascular parameters before, during and after TVT.
The above referenced related U.S. patent application Ser. Nos. 14/874,604 and 14/354,624 (now issued to U.S. Pat. No. 9,149,230) having common inventorship and ownership with the present application, disclose a multi-sensor microcatheter and a multi-sensor guidewire. These multi-sensor micro-catheters and guidewires comprise a distal end portion containing multiple optical sensors arranged for measuring blood pressure at several sensor locations, simultaneously, in real-time. Optionally, they include an optical or electrical sensor for measuring blood flow. The disclosed multi-sensor micro-catheters and multi-sensor guidewires can be configured for use in minimally invasive surgical procedures for measurement of intra-vascular pressure gradients, and more particularly, for direct measurement of a transvalvular pressure gradient within the heart, for any one of the four heart valves.
For example, a transvalvular measurement of pressure across the aortic valve, i.e. with pressure sensors positioned to measure pressure concurrently in the ascending aorta and left ventricle, allows for assessment of aortic regurgitation, before and after a TAVI procedure.
A need for improved diagnostic apparatus for right heart catheterization (RHC) and pulmonary artery (PA) catheterization has also been identified. For example, RHC may be performed in an Intensive Care Unit (ICU) for monitoring of critically ill patients. In a Cardiac Catheterization Lab (Cath Lab), RHC may be used for monitoring and diagnosis, and in the operating room (OR) for monitoring of important hemodynamic parameters during cardiac surgery or other high risk surgery.
During RHC and PA catheterization, a special balloon tipped catheter, which may be referred to as a pulmonary artery catheter (PA catheter) or a Swan Ganz (SG) catheter, is introduced through one of the larger veins, e.g. through an internal jugular vein, subclavian vein in the neck, or a median cubital vein in the arm, into the superior vena cava, or through a femoral vein into the inferior vena cava. The catheter tip is then introduced from the vena cava into the right atrium of the heart, advanced through the tricuspid valve into the right ventricle, and then through the pulmonic valve (alternatively called the pulmonary valve) into the PA, which is the main artery that carries de-oxygenated blood from the heart to the lungs. One lumen of the PA catheter extends from the proximal end to an opening at the distal tip. This lumen is fluid filled and is connected at its proximal end to an externally placed pressure transducer to enable the pressure at the distal tip to be monitored. Thus the pressure at the distal tip may be monitored by the catheter as it is advanced sequentially, firstly into the right atrium (RA), secondly into the right ventricle (RV) and thirdly into the PA. During these measurements the balloon may be partially inflated to allow the balloon to “float” and be drawn into the PA by the blood flow. Subsequently, after further inflating the balloon, the balloon is drawn by the blood flow and wedges in a smaller pulmonary blood vessel for measurement of a Pulmonary Capillary Wedge Pressure (PCWP). PCWP is an indirect measure of the left atrial pressure (LAP) and left ventricular end-diastolic pressure (LVEDP). At each point a characteristic pressure waveform is observed, and pressure measurements are recorded. That is, as the catheter tip is advanced, the observed waveform will change sequentially and show the transition from a RA pressure waveform, a RV pressure waveform, a PA pressure waveform and then a PCWP waveform.
Conventional four lumen/four port PA/SG catheters provide: one lumen for pressure monitoring at the catheter tip using an externally connected pressure transducer; a balloon inflation lumen; a thermistor lumen; and a fluid injection lumen for measurement of blood flow by thermo-dilution. The port for the pressure transducer may also be used for blood sampling, e.g. for measurement of mixed venous oxygen saturation (SvO2). Some available PA catheters include two pressure sensing lumens, which can be connected to two external pressure transducers for measurement of pressures in the right atrium and in the pulmonary artery. Advanced PA catheters or SG catheters may also include several additional lumens and ports, e.g. another port for fluid infusion, and/or one or more ports for cable connections to other types of monitoring equipment, e.g. for measurement of cardiac output, oximetry, or insertion of a cardiac pacing wire.
By way of example only, the following references provide further background information and details of insertion techniques, characteristic pressure waveforms, and indications for RHC and PA catheterization:                1) Jeremy Fernando, “Pulmonary Artery Catheters”, updated 22 Dec. 2014 (http://lifeinthefastlane.com/ccc/pulmonary-artery-catheters/);        2) “Swan-Ganz—right heart catheterization”, NIH National Library of Medicine, online Medical Encyclopedia, Update Date Aug. 12, 2014 (https://www.nlm.nih.gov/medlineplus/ency/article/003870.htm);        3) “Pulmonary artery catheter”, Wikipedia, version last modified 8 May 2016 (https://en.wikipedia.org/wiki/Pulmonary_artery_catheter);        4) “Invasive Hemodynamic Monitoring: Physiological Principles and Clinical Applications” pp. 12-15; Jan M. Headley, RN, BS, CCRN, Edwards Life Sciences; Irvine, Calif., © 2002 (http://ht.edwards.com/resourcegallery/products/swanganz/pdfs/invasivehdmph ysprincbook.pdf);        5) B. Paunovic et al., “Pulmonary Artery Catheterization”, (c) 2011, updated 3 Jan. 2016 (http://emedicine.medscape.com/article/1824547 (c) 2011);        6) “Right Heart Catheterization”, Johns Hopkins Medicine Health Library, version downloaded August 2016 (http://www.hopkinsmedicine.org/healthlibrary/test_procedures/cardiovascular /right_heart_catheterization_135,40/);        7) “Comparing FFR Tools New wires Pressure Microcatheter”, M. Kern, Cath Lab Digest, Volume 24, Issue 5, May 2016 (http://www.cathlabdigest.com/article/Comparing-FFR-Tools-New-Wires-Pressure-Microcatheter);        
Conventional balloon tipped PA catheters that use a fluid filled catheter, which is coupled to an externally placed pressure transducer, are relatively inexpensive and durable. However, they measure pressure only at a single point, i.e. at the tip of the catheter. Thus, the cardiologist must reposition the catheter, i.e. by pushing and pulling the catheter tip back and forth to position tip to make pressure measurements at different locations within the heart. During this procedure, there is some risk that repeatedly advancing and pulling-back the catheter for repositioning tip of the catheter for pressure sensing will interfere with, or disrupt, normal operation of the heart, e.g. cause cardiac arrhythmias (such as atrial or ventricular fibrillation), interfere with opening and closing of the heart valves, or risk damage to the heart tissues.
Also, pressure sensing catheters have limited accuracy. Measurements may be affected by technical limitations such as reflection of the pressure wave at the tip and distortion if the catheter is kinked or sharply bent. Inertial artefacts and slow dynamic response (time lag, damping, hysteresis, resonances, frequency filtering) can distort the waveform, in time and amplitude, as it travels through the fluid filled lumen (de Vecchi et al., “Catheter induced Errors in Pressure Measurements in Vessels: An in-vitro and numerical study” IEEE Transaction on Biomedical Engineering, Vol. 61, No. 6, June 2014). Measurement errors as much as 20 mmHg have been reported (see ref. 2 in Robert G. Grey et al., “Feasibility of In Vivo Pressure Measurement using a pressure tip catheter via transventricular puncture”, ASAIO J. 2010 56(3) 194-199. This reference also compares limitations of a Pressure Tipped Catheter (PTC) using a piezo-electric pressure sensor and a conventional fluid filled pressure sensing catheter.
Limitations of pressure sensing catheters with externally placed transducers are also discussed in United States patent application publication no. US2011/004198, to Hoch, which discloses a central venous catheter (CVC) using a piezo-electric pressure sensor. However, electrical pressure sensors of this type have some drawbacks for in vivo applications, where long thin electrical wires are carrying small electrical signals in humid environment, e.g. requirement for electrical isolation of electrical components, significant electrical drift and temperature sensitivity and electrical interference, such as, cross-talk between wires from multiple electrical sensors and from external electromagnetic sources within the operating room.
Thus, there is a need for improved or alternative PA catheters for direct measurements of cardiovascular parameters, including blood pressure measurements, during RHC and PA catheterization procedures.
An object of the present invention is to provide for improvements or alternatives to known systems and apparatus comprising multi-sensor catheters or multi-sensor guidewires.